1. Field of the Invention
This invention relates generally to the manufacture of MOS integrated circuit transistors and more specifically this invention relates to the manufacture of
MOS integrated circuit transistors having a dimension below the photolithography limitation.
2. Discussion of the Related Art
MOS transistors are used extensively in semiconductor integrated circuit devices. A typical MOS structure is shown in FIG. 1. The typical MOS structure 100 is formed on a semiconductor substrate 102. A source 106 region and a drain 108 region are formed in the semiconductor substrate 102. A gate oxide region 110 is formed on the semiconductor substrate 102. A polysilicon gate 112 is formed on the polysilicon gate 112 and oxide spacers 114 and 116 are formed on each side of the polysilicon gate 112. The gate length is represented by the distance 118 and is dependent upon the dimension 120 of the polysilicon gate 112. Because the strategic approach to improving the speed performance of MOS devices is to continuously reduce device dimensions, especially the gate lengths, it is necessary to decrease the polysilicon dimension 120. The evolution of MOS device technology has been governed mainly by device scaling and the feature size of the MOS gate length has been scaled down in the effort to increase the speed and scale of integration.
The problem with the further scaling of the MOS transistor gate length is the limitation of photolithography technology. The smallest feature size that photolithography technology can pattern is limited by optical diffraction. Current manufacturing lithography technology that uses UV or deep UV light as the light source is not able to pattern the polysilicon gate to achieve a gate length of 0.1 .mu.m and below.
One method that has been used to achieve dimensions below the limitations of the photolithography technology is a technique called over etching. However, it is very difficult to control the shape and the size of the structures when using the technique of over etching.
Therefore, what is needed is a method of manufacturing MOS transistors that achieves device dimensions below the limitations of photolithography.